Electron discharge device of the cavity resonator type



June 15, 1948. T. H. KIINMAN ETAL ELECTRON DISCHARGE DEVICE OF THE CAVITYRESONATOR TYPE Filed Sept. 6, 194a Inventors: Thomas H. Kinman, Leonard. J. Davies,

Their Attorne g.

Patented June 15, 1948 ELECTRON DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Thomas Hf Kinman and Leonard J. Davies, Rugby, England, assignors to General Electric Company, a corporation of New York Application September 6, 1946, Serial No. 695,180 In Great Britain December 8, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires December 8, 1961 4 Claims.

This invention relates to electron discharge devices of the type having resonating cavities or chambers and it is a general object of the invention to provide a device having a chamber the dimensions of which may be readily and conveniently varied for tuning purposes.

It is a further object to provide such a device in which the dimensional variations may be accomplished by means external to the hermetically sealed envelope with which the chamber is associated.

The resonating cavities or chambers employe in discharge devices of the velocity modulation type wherein oscillations are generated in the cavity by an electron beam may be mentioned as an example of the type in which the invention might find employment. Generally, such cavities are formed of hollow annular members having a circumferential slit along their portion of minimum diameter, across which slit and coaxially with the chamber the electron beam is projected. The cavity may be of generally circular or rectangular shape in cross-section as desired. In some such devices two or more resonating cavities are employed in coaxial relation with and spaced along the beam.

apertures to form the circumferential slit above referred to. The cavity is then completed by a member which connects the outer rims of the diaphragms and thus completes the hollow annular member, The envelope of the device incorporating the resonating chamber is then completed by'means of two half sections of a glass I envelope which are sealed coaxially onto the resonating cavity at each end thereof, one of them carrying the electron gun and the other the anode or collecting electrode. The electron gun has'to be so positioned that the beam is accurately coaxial with the resonating cavity.

Since the frequency at which such a device operates is dependent upon the dimensions of the resonating chamber, and since heretofore those dimensions have been relatively unalterable once the device has been completed a separate device must be constructed for practically every small frequency range to be covered.

The present invention overcomes this disadiii vantage, and enables a relatively wide range of frequencies to be covered by a single device.

According to the invention the diaphragms may have their outer edges or perimeters formed into or secured to hollow cylindrical members arranged coaxially with the electron beam and of differing diameters, the cylindrical members being electrically coupled by a hollow cylindrical sleeve the ends of which have internal diameters which are respectively equal to the external diameters of the two hollow cylindrical members. The sleeve may slide axially while maintaining contact with the two cylindrical members, and when so moved it serves to vary the eiiective dimensions of the resonating chamber and thereby to vary the frequency at which it resonates.

The sleeve may consist of a hollow cylinder having an internal diameter equal to the external diameter of the larger of the two hollow cylindrical members, and may terminate in a flange, the inside diameter of which is equal to the external diameter of the smaller of those members. Alternatively, the flange may be connected with a re-entrant sleeve capable of fitting closely on the outer surface of the smaller of the cylindri cal members. The ends of the coupling member may be longitudinally slitted to provide resilience and enable good contact to be effected between the coupling and cylindrical members.

One arrangement embodying the invention is illustrated somewhat diagrammatically in the accompanying drawing for the purpose of enabling the manner in which the invention is carried into effect to be readily understood. 1

In the drawing we have illustrated a velocity modulation electron discharge device I of known construction. This comprises a glass envelope 2 terminating at itslower end in a stem 3 from which is supported on electron gun 4. The electron gun provides a beam of electrons which is projected across a narrow slit 5 formed between the rims of apertures in the walls of a resonating chamber or cavity 5, the beam after passage across the slit 5 being returned by a reflector electrode '1 into the slit whereby oscillations at the fundamental frequency of the resonating chamber are developed therein by the reaction of the beam. The reflecting electrode 1 is supported upon a stem 8 which terminates the upper end of the envelope 2 In devices of this character as hitherto constructed, the resonating chamber consisted of two transverse walls or diaphragms 9 and m which are spaced apart by a short section II of the glass envelope, and have their external peripheral edges joined by a sleeve. Such a device will only oscillate at a, fundamental frequency determined by the dimensions of the resonating chamber. Now according to the present invention the diaphragms are made of differing diameters, 9 being larger than H], and are joined at their external edges to two cylindrical rim members l2, I3 respectively. A coupling sleeve !4 connects the cylindrical members l2 and I3 and forms the outer wall of the resonating chamber. The coupling member M has two portions of differing diameters, one of them, I5, sliding over the surface of the cylindrical member 12, while the other, 16, is adapted to slide over the member IS. The coupling member M can then be moved axially while maintaining contact with the two cylindrical members, and when so moved it serves to vary the effective dimensions of the resonating cavity ii, and thereby to vary the frequency at which it resonates. The ends of the coupling member I 4 may be longitudinally slitted as shown at H to provide resilience and. to enable a good contact to be effected between it and the cylindrical members.

The cylindrical members may be made more rigid by filling the space left between them and the adjacent Wall of the device with insulating sleeves.

The use of the invention has enabled a resonating chamber designed to rcsonatewithin a range of i5% of a given frequency to be capable of operating with a range of :20% of that frequency.

While we have shown and described a particu lar embodiment of our invention, it will be ob vious to those skilIed in the art that various changes and modifications may be made without departing from our invention in its broader as poets and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electron discharge device of the velocity modulation type comprising a cylindrical hermetically sealed envelope, a plurality of electrodes within said envelope including a cavity resonator of variable dimensions wherein oscillations are developed by the passage of an electron beam therethrough, said resonator comprising two substantially parallel walls of substantially different perimetric dimensions transverse to said envelope and each having a beam aperture coaxial with said envelope, rim members extending about the perimeters of each of said walls, said rim members being perpendicular to said walls and extending therefrom in opposite directions, and a couplin wall member surrounding said rim members and having portions slidably engaging each of said rim members whereby motion of said coupling wall member axially of said envelope varies the dimensions of the cavity formed by said parallel walls, said rim members and said coupling wall member.

2. An electron discharge device of the velocity modulation type comprising a cylindrical hermetically sealed envelope, a plurality of elecsaid envelope and each having a beam aperture coaxial with said envelope, cylindrical rim members extending about the peripheries of each of said walls, said rim members being perpendicular to said walls and extending therefrom in opposite directions, and a cylindrical wall member surrounding said rim members and having portions slidably engaging each of said rim members whereby motion of said coupling wall member axially of said envelope varies the dimensions of the cavity formed by said parallel walls, said rim members and said coup-ling wall member.

3. An electron discharge device of the velocity modulation type comprising a cylindrical hermetically sealed envelope, a plurality of electrodes within said envelope including a cavity resonator of variable dimensions wherein oscillations are developed by the passage of an electron beam therethrough, said resonator comprising two substantiall parallel walls of substantially different perimetric dimensions transverse of said envelope and each having a beam aperture coaxial with said envelope, said walls ex tending transversely through said envelope and having perimeter portions external thereto, rim members extending about the perimeter of each of said walls, said rim members being perpendicular to said walls and extending therefrom in opposite directions, and a coupling wall member external to said envelope surrounding said rim members and having portions slidably engaging each of said rim members whereby motion of said coupling wall member axially of said envelope varies the dimensions of the cavity formed by said parallel walls, said rim members and said coupling wall member.

4. An electron discharge device of the velocity modulation type comprising a cylindrical hermetically sealed envelope, a plurality of electrodes within said envelope including a cavity resonator of variable dimensions wherein oscil-- lations are developed by the passage of an electron beam therethrough, said resonator comprising two substantially circular parallel walls of substantially different diameters transverse of said envelope and each having a beam aperture coaxial with said envelope and having peripheral portions external of said envelope, cylindrical rim members extending about the peripheries of each of said walls, said rim members being perpendicular to said walls and extending therefrom in opposite directions, and a cylindrical 'wall member external to said envelope surrounding said rim members and having portions slidably engaging each of said rim members whereby motion of said coupling wall member axially of said envelope varies the dimensions of the cavity formed by said parallel walls, said rim members and said coupling wall member.

THOMAS H. KINMAN. LEONARD J. DAVIES.

REFERENCES CITED The following references are of record in the file of this patent:

UN ITED STATES PATENTS Number Name Date 2,115,521 Fritz et a1. Apr. 26, 1938 2,167,201 Dallenbach July 25, 1939 2,343,487 Steudel Mar. 7, 1944 2,353,742 McArthur July 18, 1944 

